Angular declarations和entryComponents组件有什么区别

我的app.module e.ts中有以下内容:

import { BrowserModule } from '@angular/platform-browser';
import { ErrorHandler, NgModule } from '@angular/core';
import { HttpModule, Http } from '@angular/http';
import { IonicApp, IonicErrorHandler, IonicModule } from 'ionic-angular';
import { EliteApi } from '../shared/shared';
import { MyApp } from './app.component';
import { MyTeams, Tournaments, TeamDetails, Teams, TeamHome, Standings } from '../pages/pages';

import { StatusBar } from '@ionic-native/status-bar';
import { SplashScreen } from '@ionic-native/splash-screen';

@NgModule({
    declarations: [
        MyApp,
        MyTeams,
        TeamDetails,
        Tournaments,
        Teams,
        TeamHome,
        Standings
    ],
    imports: [
        BrowserModule,
        IonicModule.forRoot(MyApp),
        HttpModule
    ],
    bootstrap: [IonicApp],
    entryComponents: [
        MyApp,
        MyTeams,
        TeamDetails,
        Tournaments,
        Teams,
        TeamHome,
        Standings
    ],
    providers: [
        HttpModule,
        StatusBar,
        SplashScreen,
        { provide: ErrorHandler, useClass: IonicErrorHandler },        
        EliteApi
    ]
})
export class AppModule { }

目前我的declarations和entryComponents都是一样的.它们包含我为应用程序构建的所有页面/组件.如果我从任何属性中删除任何条目，我会在angular2中得到错误.

我的问题是，如果它们总是相同的，那么这些属性需要什么？我想我肯定错过了一些要点.entryComponents和Declarations什么时候会不同？