Should i always call a module into a var or execute immediately in node

So, i am coming from a LAMP stack and all this new js is quite new to me.

I have written an email sending module for my little app which is executed as follows:

var emailer = require( '../../app/emailer.js');
emailer({
    tplName : 'activationEmail',
    tplVariables : {name:'john',activationLink:'bob'},
    sendToEmail: 'john@gmail.com',
    sendToName: 'John',
    fromEmail : 'noReply',
    subject: 'Activation email'
});

Now this works just fine however i am not sure what is better (as i am missing some fundamental nodejs knowledge), to run as above or run as this:

require( '../../app/emailer.js')({
    tplName : 'activationEmail',
    tplVariables : {name:'john',activationLink:'bob'},
    sendToEmail: 'john@gmail.com',
    sendToName: 'John',
    fromEmail : 'noReply',
    subject: 'Activation email'
});

As you can see here this is triggereing an activation email, the emailer module is being called from within a passport module.

My question, should I 'require' the module into a var then reference the var later, or require the emailer module each time i need it.. i'm not sure what the difference is..

A NooB Q i know, but i can't find a solid answer on google.

Thanks in advance, John