Open a client, then Preferences. Two switches here change what your client can do in their own app, so it is worth knowing exactly what each does before you touch it.
Nutrition logging
Workout Titan Coaching describes this as enabling detailed meal and calorie tracking. On, and your client can log food and you can see it. Off, and they cannot. Your view of their nutrition reads "Nutrition logging turned off for this client", and the client is told they cannot log nutritional intake.
Leave it off for clients you train but do not advise on food. Turning it on for someone who will not use it just puts an empty diary in front of them.
Weight logging
Described as allowing the client to log weight and share progress. Off, and the weight screen in their app is visible but disabled, telling them weight logging is managed by their coach.
This one deserves thought rather than a default. Daily weighing is unhelpful for some people and actively harmful for a few, and taking the scale out of a client's hands is a legitimate coaching decision. It is also one they will notice, so tell them you have done it and why. The message on their side points them straight back at you to ask.
You can still log weight for them from their profile while the switch is off.
Measurements are always yours
There is no switch for this one. Clients can never log their own body measurements, and the measurements screen states that plainly. Chest, waist, hips, arms, thighs: all of it is recorded by you.
That is a reasonable design decision rather than an oversight. Self-measured circumferences are inconsistent. Tape tension, placement and posture move the number more than the body does, so a series taken by one person is worth far more than a series taken by whoever happened to have the tape.
What this looks like in Nutrition
If your client also uses Workout Titan Nutrition, these preferences reach across. With nutrition sharing on there, their calorie and macro goals show as managed by you and cannot be edited on their side, and weight logging follows the switch above.
One thing worth knowing: sharing is the client's switch, not yours. If they turn nutrition sharing off in their own Manage account, you stop seeing new logs and they take their goals back. Nothing they logged while disconnected is ever shared retroactively.
If a change will not save
You will see an error rather than a silent failure, and nothing is half-applied. Check your connection and try again.