What I do is pull the tube almost all the way out. Using the keg as a fulcrum (look it up...) leave about 2-3 inches of the tube in the keg and slowly pull the dip tube toward you to give it a slight bend. Insert the tube another 2-4 inches and repeat. Do this about 3-4 times and the tube won't be near the bottom any more.
Be sure to check the tube (try to pull it out) to make sure it can be removed. If not, then you bent it too far. You'll have to try to bend it straight inside the keg.
I got a bunch of kegs in a deal and after disassembling all of them, I realized I mix and matched a few parts... My very first kegged batch was just giving me a quick spray then nothing... Realized the dip tube I used was actually touching the bottom of the keg, so I took about 1/4" off of it... That is the only one I have cut...
Dip tube cutting is more prevalent in the US than in most Europe. It is a cultural thing apparently. Used to be done for hygiene purposes but now it is mostly for cosmetic reasons. It doesn't perform any differently really either way.
I was wondering the same thing. When I emptied my last keg there just barely a few globs of sediement around the bottom of the keg. i was wondering if that could be the off flavor I was picking up. I never really noticed the 1st pint or 2 having a lot of sediment in them as I assumed they would from sucking it all up.