I always do this! All of my Pokemon have to be on the same level, or at least one level apart. For example, I have a team of level 47 Pokemon. I train one of them to level 48, followed by another, and another and so on until all of them are level 48, and the process starts all over again. The first Pokemon to get trained up a level must have the least amount of XP left till level up, followed by the second least amount and so on; that's the way I train. I do this throughout the game starting from the minute when I capture my first Pokemon up to the Elite 4, not only at certain points. I make it a point to give an even and fair share during training so that everyone has an equal stand in my team, not being different levels and having inconveniences to higher-levelled opponents.