This can apply to first playthroughs or replays or both.
Pretty much since gen 4 I tend to start a Pokemon game knowing what Pokemon I want, usually even what moves I give them for maximum coverage. I prefer to not waste time in mons that I know I'll dump in 2-3 badges, with rare exceptions like not having any Pokemon or moves strong against key trainers. Sometimes I'll realize mid-play acquiring a certain Pokemon isn't worth it (one time I got a Slowking instead of a Slowbro when I realized how bad Slowpoke's stats are until it evolves at level 37), but the vast majority I start with a full game plan in mind and stick to it. Teambuilding and organizing is one of my favorite things about the series so it's satisfying when you catch your final Pokemon to complete your plan.
Pretty much since gen 4 I tend to start a Pokemon game knowing what Pokemon I want, usually even what moves I give them for maximum coverage. I prefer to not waste time in mons that I know I'll dump in 2-3 badges, with rare exceptions like not having any Pokemon or moves strong against key trainers. Sometimes I'll realize mid-play acquiring a certain Pokemon isn't worth it (one time I got a Slowking instead of a Slowbro when I realized how bad Slowpoke's stats are until it evolves at level 37), but the vast majority I start with a full game plan in mind and stick to it. Teambuilding and organizing is one of my favorite things about the series so it's satisfying when you catch your final Pokemon to complete your plan.