Cross versus isolated margin
Choosing a margin mode is choosing what can be lost when a position goes wrong: the margin you assigned, or the account.
Isolated margin
Only the margin allocated to the position is at risk. The liquidation price is known at open and does not move unless you add margin.
The cost is capital efficiency: margin sitting behind one position cannot support another.
Cross margin
The whole account balance backs every cross position. Liquidation prices are further away, which is why it feels safer, and a single bad position can take the account, which is why it is not.
On a wallet page, the cross and isolated split is shown alongside the closest liquidation, because the two together describe the real exposure.