My personal opinion is that training with a partner is somewhat counter-intuitive, as it relates to the world of triathlon. I feel that it is such and individual sport, that there needs to be a huge amount of time spent training by yourself so you know how to perform on race day...by yourself. However, there are some great benefits to training with somebody, or a group of people.
The main benefit that I get out of scheduling a training session with a training partner (which is almost always The Captain, who just started his own blog! Check it out here), is that it greatly reduces the chance of skipping a workout. If you have someone that you are meeting up with, it's pretty tough to cancel on them, as opposed to when it is just yourself and you can make up excuse after excuse as to why you should skip a workout. The other huge benefit that I get out of training with other people is that you may be able to push yourself a little more than you expected. I know that if there's a day when I'm not feeling to into a workout, and I happen to be training with The Captain, it's very easy to feed off of his energy and I quickly find myself excited about the workout that we're doing! Also, there's been a number of times where we find ourselves quietly competing with each other, but not acknowledging it. For example, we'll push the tempo on a bike ride a little harder than we normally would to see who needs to pull it back first, which typically provides a really good workout!
What happens to work best for me is to schedule early morning workouts with my training partner. The early morning in Arizona is probably the best time to get a workout in without the temperature reaching 110 degrees. It's also the time of day that takes away the least amount of family time. If I am not meeting The Captain, it's very easy for me to hit the snooze button and get that extra hour or two of sleep. And as much as I know all of this, there's still times when I do hit that snooze button, and hate myself all day for doing it. So again, my advice is to periodically schedule your workouts with a training partner. And if you don't know any, let me know and maybe I'll be your new training partner (if you don't mind going for long bike rides starting at 5 a.m.!)