A very dumb view

[Octavian]

Use the supplied Lens hood with the L
This craic of taking on and off the filter isnt it just like on an off the lens cap!!??   
if you know you are going to a sea side shot where there is misty water in the air etc etc then ya chuck on a filter so you can just wipe the lens as often as you like without worryig about scratching the front glass! apart from that on good weather days away from any blowing clay or sand in the air maybe give it a miss!

[Chris_prophotographic]

My  FILTER saved my lens from a nasty knock, so yeah USE THEM and the HOOD its its not too much bulk (say 70-200 hood and below)

[AvTvM]

I use high-grade, multi-coated, clear, NON-UV protection filters on all my better lnses.
Hoya HD or Pro1 Digital Protector or B&W 007 clear MRC.
I avoid UV-filters, they are unnecessary and may degrade image quality slightly. The cheap ones will for sure.

I take my hi-grade protection filters only ever off the lens, when I use another filter - circular pol filter, ND or ND grad.

I also take them off in dark conditions wehn tehre are point-light sources in the frame - that's the only time I ever saw a possible negative effect on image quality ... reflections / ghosting. If you pay attention, you will see it in the viewfinder and take the filter off in good time.

I am amazed how much drig and dirt regularly accumulates on the front of these filters, although I treat my lenses rather well. Air in our cities is not as clean as you would like tit to be .. is all I am saying. Not even to mention really harsh environments with mist, spray, beaches or on the tarmac of an airport next to a 747 being de-iced with huge amounts of orange de-icing agent ... with a good filter .. you just wipe it off. Way easier to clean than lens front elements. 

But .. your mileage will vary ... if you never leave the clean room, you won't need protetcive filters. :-)

[sandymandy]

without worrying about scratching the front glass!

Who is cleaning his L lens in such an akward way that there might be scratches? Sandpaper cleaning?

[pierceography]

I use high grade UV filters for protection.  I realize there might be a slight loss in IQ, but to me it's all about piece of mind.  I'm not a professional, so my gear was bought with money I had to save and thus I take VERY good care of it.  I'm willing to accept a very slight loss in IQ if that means I'm not constantly worrying about scratching a piece of L glass or bumping it into something.

As many have said, I'd rather break a $100 filter than a $2,500 lens.

[drjlo]

IMO, if you want protection, ditch those awkward Canon lens caps for the double-center-pinch lens caps from eBay, which are far easier to cap/recap.  Keep them on the lens when not in use, or keep the hood on. 

Good quality UV filters are fine for IQ in daytime, but point at high-contrast scene/light especially at night, and the reflections are very easy to see on photos. 

[Random Orbits]

My  FILTER saved my lens from a nasty knock, so yeah USE THEM and the HOOD its its not too much bulk (say 70-200 hood and below)

+1.  Although wide angle lens hoods are almost pointless for protection.

How many people use hoods indoors?

[BL]

+1.  Although wide angle lens hoods are almost pointless for protection.

+1.  especially for WA zooms since they take up way too much real estate in the bag

How many people use hoods indoors?

all the time.  i take family portraits and without fail, every lens is grabbed at one point in time by a well meaning toddler or child wanting to look through the business end of my 85L or 70-200L

[comsense]

without worrying about scratching the front glass!

Who is cleaning his L lens in such an akward way that there might be scratches? Sandpaper cleaning?

You will be surprised to know that invisible crystals in dust could be very effective sandpapers without your knowledge. Best not to get into situation where you have to clean good optics. At the very least it takes too much effort and time to do it right, which is not always at hand.