Money laundering is typically tied illegal behavior, things such as tax evasion, extortion, trafficking, etc. Having the means to deal with money laundering helps inhibit the illegal activity tied to it.
Assuming that you're an average Belgian, the effect of money laundering is that you pay taxes while the criminals don't, so the money that your government could and would have spent in things that benefit you gets stolen instead.
Less money laundering would mean that you could either get more gov't services or lower taxes.