Hmm, interesting thread.
Well, in my situation, I tend to avoid Pokemon as I make my travels across the region. Now, especially in situations such as Victory Road, I will be
bent on avoiding Pokemon, so I often buy Max Repels to keep them at bay. (Not that they always work!) Such journeys that can be tedious such as cave travel in some of the Pokemon games, are where I really utilize my avoidance strategy. As for avoiding specific Pokemon, I tend to stay away from Rock Type Pokemon, just because they tend to be hard to take down, especially in cave situations that take me 30 minutes on average to complete.
I don't avoid Pokemon in all cases, though. I always frolic in the tall grass on those days where I'm training Pokemon. For example, my Heartgold team has an average level of 33 or so, but my stubborn Golbat refuses to level up at a nice rate! (He's a level 28.) In those cases, I'll spend hours trying to train my team in the tall grass. I also go out of my way for Pokemon for another obvious reason:
To Catch 'em All! There comes those days when some members of my team just fall behind, and a new member must join the ranks of Mido. In those important events, one must traverse into the grass to find Pokemon.
I mean, why not? It's free experience! And the game assumes you will gain experience on your way to the next town because the bosses are more difficult and your rival's pokemon are leveled up a decent amount the next time you see him. Not fighting wild pokemon is wasteful. Especially when each one takes less than a minute except when you're just starting and the fights are pretty close.
