Meditation on an object(concentration for the sake of the discussion) ,dharana,could be used as a tool to lead to meditation on no object,dhyana ( thoughtless state,pure bliss,just self,or mind perhaps ,conciousness) leading eventually to complete dissolution of self or what some might call non-dual awareness & non-separation, resting in pure awareness perhaps-samadhi.
practicing dharana,dhyana(limbs 6&7 for simplicity’s sake) can allow the yamas and niyamas (limbs 1&2,then) for instance to open up and arise natturally.
The interconnectedness of all the limbs can demonstarte how practicing one can open up them all.The practice of active surrender in meditation coulld be accessed through using concentration as a tool. So the niyama ,Isvhanidharma, loosely defined here for asake of discussion here as’ living with awareness of and surrrendering to the divine ’ intersects quite well with (the esssence of) limb7- dyhana-i.e surrenderdering the self,awareness,
really i think the modern patanjali apporach is to tackle all the limbs together rather than try to ascend them as if they were a staircase ,step by step. if we tackle them all itogether progress is easier such that integration of all 8 is wiser.( the practice of any limb will hit an obstacle if any other limb is excluded) The sum is greater than the parts, after all.
So to the OP- concentration could be used as a tool to empty the mind eventually(i.e including the practice of concentration itself) ,resulting in a state of surrender.
1.Meditation on or with object(‘concentration’ for the sake of discussion though for soe reason i either don’t like that word or i feel cocnetration is not desirable, as in yoga one is heading towards an effortless state, one of surrender, so it may just be used as a tool or vehicle in that sense)—>
2.<—Meditation without object(thoughtless state,pure bliss etc)–>
3.<—Dissolution of self completely( cosmic conciousness,samsadhi or whatever)
Also pratyahara is quite useful important as like a gateway limb(between the first 4 limbs and the last 3) in that sensory introversion open us up internally and externally so the two eventually merge ,our supposed sense of outer and inner, or “I” and other.It certainly expands our sense of inner self and our expansive nature which can help to really open us up,inwards (first)and then expanding outwards…
Looking at yoga as a system for self-transformation with the help of the lense of science and and perhaps developments like quantum physics may help to open up this otherwisse vast esoteric, and at times hazy field buried in acient and arcane texts (and direct transmission from teacher to student , a lucky few who in some sense ‘initiated’ and committed ,so to speak , through the ages). It’s is a very anciennt vast wisdom but to alot of people it’s often not that accessible which is a pity.