Yes, it will alter your intonation truout the neck, give you a more dead tone, cause you to have dirty fingers, causes gunk all over the fret and fretboard, cause you to not practice more because your out of tune and your not playing with a good tone, you keep in the bag/case/storeroom, you forget about it saying that guitar is hard or I'm not a good musician, you pick up computer games that accomplished nothing for you in your life, and you get a job and you get married, have some kids, a few pets, finish paying for your flat, drink some kopi, then die.
Moral? Change your strings regularly.
I used to changed every week. Some dudes do change it every other day, and their not professionals. Pros can change it even after every take in a recording session.
Have a good personal benchmark. When you start sounding normal, then dull, then "sigh must play/practice guitar", please go and change your strings. Personally I change them when my tone changes, and if I'm conveniently located at Guitar 77 for my strings and the only strings I will use thus far. I'm not so crazy.
There are products to keep your strings fresher and longer, and do put in then half minute more effort of packing up your gear and cleaning the strings after your done.