Unfortunately this 300,000 conscripts is not really a big deal. Consider
https://www.understandingwar.org/backgro...bilization. In 2021 Russia drafted 261,000 men from a pool of 1.2 million available candidates. These "troops" serve for one year. In Soviet times the draft was for two years. The joke was that the duty of conscripts in their first year was to be abused by the conscripts who were in their second year. Similarly, the duty of conscripts in their second year was to abuse the conscripts in their first year. Now, since there are no second-year conscripts, nobody does anything. The conscripts get almost no real military training and pretty much can't do anything but manual labor. Fortunately, given the Russian army's poor logistics, plenty of manual labor is needed.
In theory, Putin can get most of his 300,000 "new" conscripts simply by not releasing the "class of 2021", which I am sure is the plan. Unfortunately, quite a few of them got themselves killed, but at least 200K remain. In theory, Putin can get himself another 500K or so troops simply by recalling the class of 2020 and the class of 2019. These "troops" are presumably the ones that have had the most recent "training". I suspect it is going to be pretty hard to round up all those guys, but it can probably be done "well enough" to net at least 100K troops. That is 300K "additional" conscripts and it only affects 19-22 year olds. It really doesn't affect all that many of them either, about 300K out of 3.6 million such people.
The "big deal" in this new conscription effort is that Putin doesn't have to release any years conscripts after a year. That "ramps up" the Russian military by 260K a year with no increase in conscription. The other factor is that by declaring the Donbas and Kherson Oblast as part of Russia, Putin can send these conscripts there and they can't refuse, which until now they could. This is what really "matters" in the new regulations.
I think nobody should believe that this will not be a net plus for the Russian military. It will allow them to compensate for their manpower intensive logistics chain to a large extent. It will also release more competent troops who are now used in the GLOCs. This group will slightly increase Russia's military capability directly. They are doing it for a reason.
That said, there are certainly down sides. First, these conscripts will suffer casualties, probably disproportionately to their numbers and job description, because they lack training and discipline. These losses will get noticed by society. Putin will of course try to at least delay if not prevent the information from being spread, but it will be spread. Second, these conscripts themselves need food, fuel, and shelter. That adds to the logistics burden. Third, these conscripts will have even lower morale than the Russian soldiers. They will also be unable to react quickly to battlefield reverses or successes. A Ukrainian breakthrough like the recent one would result in massive KIA/POW statistics of guys who didn't get the word and wouldn't know what to do if they did.
