Adjusted EBITDA

Wanted to see if reasoning for the following question is fair:

Why for adjusted EBITDA do you add in SBC, one time, non-recurring stuff, D&A, while for UFCF you add D&A and recalculate EBIT to avoid one-time expenses on the I/S, but don't add back one time expenses, such as restructuring fees, SBC, impairment charges as seen in CFO?

1) Is this because adjusted EBITDA as described above is really measuring cash flow available prior to capex, NWC, cash interest and taxes, and mandatory repayments adjustments? On the other hand, UFCF, as describe above, is for the purposes of valuing the business's core operations?

2) Is this is a good formula to get a sense of how much cash is available to service additional debt:

Adjusted EBITDA - Cash Taxes - Cash Interest - CapEx - Inc. NWC - Mandatory Debt Payments

Would using CFO - CapEx - Mandatory Debt be better? Any better formulas?

Thank you. Appreciated.