hand solo which a/c was you flying before, a BOEING ? Don't take this question too serious.
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Basicly, to use all the benefits of this highly sophisticated, excellent AIRBUS you final aime should be, trying to fly managed as long as possible and as long as practicable, means if traffic situation permits. This is the way this aircraft is designed for !
Of course deviating from the managed profile, due to short-cuts etc and you find youself high on profile you have to use basic skills, means use rawdata informations to check altitude against remaining track miles, as mentioned in previous posts and act accordingly. BUT there is not only one way to fly.
The DECEL information is a very conservative helpful information. You can trust on it, or if you don't for whatsoever reason, I don't know, it's in any case a useful information you should not just disregard.
All the stuff concerning CONFIG changes is "basicly" a matter of your landing weight, which results in different dynamic energies.
There is no BASIC RULE how to DECEL, like on old aircrafts maybe (e.g. at 20nm dot this, at 10nm do this and so on) - AIRBUS flying is something very dynamic and good AIRBUS pilots are flexibel and open minded to cope with different situations and use ALL the build-in features provided to the pilots.
There is NOT only ONE way to fly the AIRBUS.
Flying, I should better say to configer e.g. an A321 close to MLW for landing is completely different, then an A320 with almoust zero load.
In the first case it is not bad so select FLAPS 1 in an early stage of approach, in the 2nd case it might be well sufficient to start the configuration changes while intercepting the G/S for example or even later.
But, to be honest, I am "managed-minded", and I like and try to fly in MANAGED mode as long as possible using this excellent FMGS, it's sometimes a kind of challenge to fly MANAGED and to use the FMGC as the only interface to the aircraft systems, although sometimes it would be easier to to call just for HDG PULL or SPEED PULL etc. like on the old a/c like a B... or so
So if you have the chance to fly the entire approach down to the landing fully MANAGED, you may observe that it works perfect. A great aircraft.