We started doing tryouts about 6-7 years ago with some very lenient marks which are essentially designed to demonstrated a very basic level of fitness. At one point, we were getting 200-230 people trying out for spring track, 180-200 for winter track, and 70-100 for cross country. These numbers were usually including a group of athletes, up to 40%, who were never in shape, not overly interested in being competitive, or decided to do track/cross country at the last minute for social reasons or to put on their resume. This size was difficult to adequate provide feedback to, coach, and maintain safety. Now, with tryouts, we generally get about 60-80 for cross country, 120-150 for winter track, and about 140-160 for spring track.
We generally only end up cutting maybe 2-5 kids per season, and even then it is after a probationary period to give them a second chance. Overall, it is not perfect, but it has allowed our staff to maintain a team size that is managable, and a roster who is at least minimally motivated. It also gives the runners a bit of incentive to maintain fitness over the summer and/or off-season.
For cross country, we do a two mile time trial (at Burke Lake), with a different standard for upperclassman vs. freshman, boys & girls). For winter and spring track, we have them do 2 "consecutive" events from the following: 100m, 200m, 400m, 800m and 1600m. They must hit one of the two standards minimum. We do not cut freshman, but if they miss the standard, they must hit it before the first meet, to demonstrate that they are ready to compete.
I'd never cut anyone as you never know how they'll turn out months and years later.
Eventually, though, they do cut themselves if they're not keeping up.
I always figured if they come to practice every day and try, then they're on the team. However, if they skip practice or would rather screw around, then we let them go.
One local high school team had these standards (instilled due to huge numbers of athletes), at a 2-mile time trial on first day of school:
Girls: 20:00
Guys: 18:00
They also got a second chance one week, or maybe 10 days, later before being told to try again the next year.