@@MAX_CONNECTIONS: it returns maximum number of synchronous user connection allowed. SQL Server allowed by default maximum 32767 connections. To avoid many connections it can be configured at server level.
Note: Maximum connections (32767) is depend on application and server hardware limits.
@@CONNECTIONS: It's returns number of connection attempt on SQL Server since SQL Server has been started.
SELECT [ConnectionAttempts] = @@CONNECTIONS,
[MaximumAllowed] = @@MAX_CONNECTIONS