Using a syringe and hose to remove fluids

Seen this on Mighty Car Mods and probably not the professional way of do things. For putting in new coolant, brake fluid etc they got a large syringe and attached a bit of hose piping to it and then suck out the fluids and then clearly put new fluid in.

Is this even a suitable method or should a full flush of the system not be carried out?

Seems a decent wee trick and if I were to ever try this method, I thought I would ask for opinions first.

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