all you want is to see how fast any given load is going, then no, you don't need a chrono.
If you want to know everything you can about those loads, then you do need one.
You take a manual specific load, match the components as good as you can. BUT the velocities are all over the place, along with terrible groups, you have something wrong with your loading practices. It could be as simple as mixed headstamp brass. Or a powder charger that is dropping inconsistent charges. Or-or-or a bunch of other things. CONSISTENCY
is the name of the game for a lot of things, but handloading it is of most importance. A chrono will tell you that.
Now you're loading for a high powered rifle, a classic bottlenecked case. You want to drive a premium bonded bullet at the highest velocity you can. Shooting over a chrono will tell you when any given powder is running into it's highest working pressure. Loading rounds that increase the powder charge the same increment as you work up the load, you will see the gain in velocity for each higher powder charge start to fall off. More pressure, but not more velocity. If you push it even higher, the velocity can actually go DOWN-decrease! How would you know that without a chrono?
Knowing the velocity of a rifle bullet will allow you to calculate downrange bullet drop. Along with the ballistic coefficient , the calculation can be figured. Using the book value, or what they claim it SHOULD be may be all wrong. You may have a "slow barrel". Like my Ruger .280. A 140 grain ballistic tip was supposed
to be going 2950 fps. Over my chrono, it was actually 2650!
It killed deer DRT at close ranges of under 100 yards, but a long shot of 350+ missed low. Good rest, relaxed, should have hit him. That's when I actually checked the velocity.