Communication and coordination is key.
HS is HS and no Travel Ball, period. Spring Only. Summer/Fall is Travel Ball, No HS imposed restrictions or activity outside of the class if single sport, or not even an option for Football/Basketball. If pitcher, you had to communicate with HS coach about throwing during the week and what travel events we had on the books during the fall (class workouts, etc). Just make sure everyone is aware and on the same page and not over tax the arm during the week.
I do see the "money" sharks in the water with early season events and showcases, but HS season is hands off for Travel ball, unless worked out with HS coach beforehand. I know there are some World Showcases or other money makers like MLK tourneys, or Pitcher/Catcher showcase in Iowa in March, but those interfere with rest and/or ramp up for or in season play for HS season, so they have always been a no go. No Travel events until May, after Districts, etc.
HS, in general, also tried to limit outside lessons or workouts, which I understand, but with proper communication and line of sight, everyone can play nicely. My son has used the same Pitching Coach and HIT facility (speed/strength) for years, played elite national level travel ball since early on and that is what got him the reps, experience, exposure and competition to make it to the level of play when he showed up on campus as a Freshman. We did not stop those lessons or workouts but coordinated those with HS Coach (even invited him to pitching lessons in Fall) to see and participate, and be informed. Even added him to Gamechanger of Travel Team for awareness and activity. Son also asked for permission in the fall to attend the HIT workouts instead of off-season class, after school or later workouts. We also coordinated with the 1 PC on rest, load, and availability throughout the on and off seasons, HS or Travel events, usage, and schedule.
Different strokes for different folks and in different regions. Your results or focus and priority may differ, but HS is a time for my son to play with his friends (as most or many don't and haven't play regular or elite travel), represent his school and community with pride and get good reps to get/stay in shape and healthy for and to ramp for Summer/Fall, Travel ball and events. etc.
If HS would have been overbearing or too restrictive in the off-seasons, he said he would have passed and focused on Travel Ball only. But we had good relationship with the Varsity Coach from Freshman year onward and it worked and it continues to work out for everyone.